There are many types of topical antiperspirant products that are commercially available or otherwise known in the antiperspirant art. Most of those products are formulated as sprays, roll-on liquids, creams, or solid sticks, and comprise an astringent material, e.g. zirconium or aluminum salts, incorporated into a suitable topical carrier. These products are designed to provide effective perspiration and odor control while also being cosmetically acceptable during and after application onto the axillary area or other areas of the skin.
Within this product group, antiperspirant creams have become increasingly more popular as an effective alternative to antiperspirant sprays and solid sticks. These creams can be applied by conventional means, or packaged into topical dispensers to make topical application more efficient and less messy. Perspiration and odor control provided by these products can be excellent. Many of these creams, however, are cosmetically unacceptable to a large number of antiperspirant users. Application of these creams can be less messy, difficult to spread and wash off, and even when a cream applicator is employed, the applied areas often feel wet or sticky for several minutes after application. These compositions are especially difficult to uniformly spread over hairy areas of the skin. Many consumers have therefore preferred antiperspirant sticks for ease of administration and drier skin feel immediately after application, although the antiperspirant sticks typically leave an undesirably high residue on the skin.
One method for making improved antiperspirant creams involves the formulation of particulate antiperspirant actives in a mixture of volatile and nonvolatile silicones or other carriers. The use of such volatile solvents in these mixtures helps reduce stickiness, improve dry-down times after application onto skin, improve ease of spreading, and improve wash-off characteristics. To maintain physical stability of these creams, however, inorganic thickening agents such as bentonite clays, hectorite clays, colloidal or fumed silicas are often needed. The inorganic thickening agents, however, contribute a grainy texture to the product and are not especially effective in maintaining physical stability when higher concentrations of volatile silicone or nonsilicone solvents, or lower viscosity nonvolatile silicone or nonsilicone solvents are used. This physical instability results in solvent syneresis (weeping of solvent from the cream matrix) during packaging, storage or shipping.
Product instability in the form of solvent syneresis can be minimized or eliminated in these soft creams by simply formulating the product into a harder, more conventional, antiperspirant stick. Many consumers, however, prefer the lower residue cosmetics associated with the soft creams, especially when these creams are applied with a cream applicator device having a perforated cap through which the soft cream is extruded and applied to the skin. Antiperspirant sticks are too hard to be extruded through most perforated caps, and typically result in higher visible residue on the skin than soft antiperspirant creams.
Other methods of preparing soft antiperspirant creams involve compositions comprising a volatile silicone solvent, suitable gellant, and antiperspirant active, which compositions are prepared by select processing methods. Components of the compositions are mixed together and heated above the melt point of the gellant, and then cooled to below the normal solidification point of the composition while subjecting the composition to continuous mixing or shear. The continuous mixing or shear prevents the product from forming a solid matrix at its normal solidification point, and thus forms a soft creamy matrix with continuous mixing below its normal solidification point. The continuous mixing thus prevents the composition from solidifying into a harder gel stick, and thus transforms it into a soft cream instead. These compositions, however, tend to be physically unstable during storage and result in substantial solvent syneresis during storage, shipping or even during application of the soft cream when applied through a perforated cap.
It has now been found that new antiperspirant creams can be prepared that deliver improved cosmetics, product stability, and reduced solvent syneresis, without reliance on the use of inorganic or polymeric thickening agents. The new antiperspirant creams are anhydrous systems that are substantially free of inorganic or polymeric thickening agents, wherein the composition has a penetration force value of from about 75 grams-force to about 500 grams-force, a delta stress value of from about 300 dyne/cm.sup.2 to about 8,000 dyne/cm.sup.2 as measured after extrusion of the composition through a shear force delivery means, and a static yield stress value of at least about 1,000 dyne/cm.sup.2 as measured after extrusion of the composition through a shear force delivery means. These creams are soft enough for application through a mesh top or other perforated application cap but act as antiperspirant sticks in having minimal or no syneresis during storage. When stress is applied to the new antiperspirant creams, preferably by extruding the cream through a perforated cap or other shear force delivery means, prior to application, the cream becomes more fluid-like and easier to apply topically to the skin. These improved creams are effective at maintaining product stability and minimizing solvent syneresis, especially when used in combination with higher concentrations of volatile solvents or lower viscosity nonvolatile solvents.
It has also been found that these anhydrous antiperspirant creams are especially effective when prepared by select processing methods. In particular, it has been found that these creams can be made by 1) preparing a flowable liquid composition containing from about 5% to about 35% by weight of a particulate antiperspirant active, from about 0.1% to about 20% by weight of a crystalline gellant, and from about 10% to about 80% of an anhydrous liquid carrier for the crystalline gellant having a solubility parameter of from about 3 to about 13; and 2) solidifying the flowable composition without application of continuous shear force at or beyond the point of solidification, wherein the solidified composition is substantially free or inorganic or polymeric thickening agents, and has a penetration force value of from about 75 gram-force to about 500 gram-force, a delta stress value of from about 300 dyne/cm.sup.2 to about 8,000 dyne/cm.sup.2 as measured after extrusion of the composition through a shear force delivery means, and a static yield stress value of at least about 1,000 dyne/cm.sup.2 as measured after extrusion of the composition through a shear force delivery means.
It is therefore an object of the present invention to provide an anhydrous antiperspirant cream composition with improved stability and spreading performance that is substantially free of inorganic or polymeric thickening agents. It is yet another object of the present invention to provide such a composition in combination with a perforated cap or other shear force delivery means which provides for improved topical application of the composition onto skin. It is also an object of the present invention to provide a method for preparing such improved antiperspirant cream compositions.